1. Field of Invention
The present invention relates to a tape measure, and more particularly to a reel rotation mount arrangement equipped with friction reduction means for tape measure, which is capable of not only substantially supporting a tape reel via a supporting axle but also enhancing the rotational movement of the tape reel by means of the friction reduction device.
2. Description of Related Arts
Retractable tape measures have been commercially used for many years. As shown FIG. 1, a conventional tape measure comprises a housing A1 having an entrance and two opposed sidewalls A11, a reel A2 rotatably mounted in the housing A1, an elongated measuring blade A3 having one end attached to the reel and another stopper end extending out of the housing A1 through the entrance, and a retracting means A4 for winding up the measuring blade A3 in a coil rolled manner in the housing A1 while the stopper end of the measuring blade A3 being blocked at the entrance of housing A1. One of the most distinctive features of the tape measure is that the measuring blade A3 can be pulled out from the housing A1 for measuring purpose and automatically retracted back into the housing A1 via the retracting means A4.
In order to rotatably support the reel A2 in the housing A1, the tape measure further comprises a supporting unit comprising two hollow supporting shafts A5 integrally and inwardly extended from the two sidewalls A11 of the housing A1 respectively to rotatably support the reel A2. Accordingly, since the housing A1 is usually made of plastic to reduce the cost of the tape measure, the plastic made supporting shafts A5 cannot rigidly support the reel A2. Especially when the pulling force and the retracting force from the measuring blade A3 are exerted on the supporting shafts A5, the supporting shafts A5 will be broken easily. Moreover, since both the supporting shafts A5 and the reel A2 are made of plastic, the frictional force between the supporting shaft A5 and the reel A2 will generate heat and wear away the supporting shafts A5, so as to deteriorate the smooth operation of the measuring blade A3.
For reducing the frictional force of the tape measure, a bearing A6 is mounted between the supporting shafts A5 and the reel A2 since the bearing A6 is commonly used as a friction reduction device between the two rotational surfaces to reduce the friction force therebetween. However, there are several drawbacks for the tape measure when the bearing unit A6 is employed therewith.
Since the contacting area between the supporting shafts A5 and the reel A2 is constructed as an outer circumference surface of each supporting shaft A5, the bearing A6 must be radially extended to cover the contacting area in order to enhance the rotational movement of the reel A2. In other words, a bigger interior of the housing A1 is required to fit the bearing A6 therein, so that the size of the housing A1 must be substantially increased, so as to reduce the portability of the tape measure.
In addition, even though the bearing A6 can enhance the smooth in and out sliding movement of the measuring blade A3 with respect to the reel A2, the structure of the bearing A6 will cause a vibration force on the measuring blade A3. It is because two sides of the reel A2 are rotatably supported by the supporting shafts A5 respectively, when the measuring blade A3 is pulled out from or retracted back to the housing A1, an uneven pulling or retracting force is created at two sides of the reel A2. As a result, the sliding operation of the measuring blade A3 is deteriorated by the vibration force.
Moreover, the bearing A6 will not only increase the cost of the tape measure but also complicate the structure of the tape measure so as to increase the manufacturing cost thereof. Therefore, the conventional tap measure cannot provide a rigid structure to support the reel and a smooth sliding operation of the measuring blade A3 while being cost effective.
Another drawback of the conventional tape measure is that the retracting means A4 is easily broken by the in and out movement of the measuring blade A3. When a portion of the measuring blade A3 is pulled out from the housing A1 through the entrance thereof, a retracting force is restored in the retracting means A4 for automatically retracting the measuring blade A3 back into the housing A1 when the pulling force on the measuring blade A3 is released. However, when the measuring blade A3 is pulled outwardly, the weight of the measuring blade A3 will be dropped downwardly and force the measuring blade A3 in contact with the housing A1 at the entrance. Therefore, the retracting means A4 must provide enough retracting force to not only pull back the measuring blade A3 into the housing A1 but also compensate the friction force between the measuring blade A3 and the housing A1. In other words, due to the friction force, the retracting means A4 will be easily worn out after a period of continuous use.